Classification of inspection grades for low-temperature pipelines
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GB/T20801.1-2025 Classification of inspection grades for industrial pressure pipelines, Clause 8.3.1.2: Pressure pipelines that meet one of the following conditions are assigned to Grade I for inspection: … d) Ferritic pipelines with a design temperature below -46°C； (Newly added in this clause)…GB 50184-2011 Code for Acceptance of Construction Quality of Industrial Metal Piping Projects applies to low-temperature pipelines with a design temperature below -20°C. SH/T 3501-2021 Code for Construction and Acceptance of Steel Piping Projects for Toxic and Flammable Media in the Petrochemical Industry: Low-temperature pipelines with a design temperature below -29°C. For a petrochemical project that is not related to petroleum processing, what should be the inspection level for pipelines operating at -25°C?
From the perspective of the standard provisions, special attention indeed needs to be paid to the classification of inspection grades for low-temperature pipelines. Regarding the addition of ferritic pipes with a design temperature below -46°C to Category I inspections, it is recommended to pay close attention to the following key practical aspects: Material verification: Special attention should be paid to the Charpy impact test data of the materials in low-temperature environments; it is advisable to check whether the low-temperature toughness parameters of the pipe materials meet the requirements specified in GB/T 20801.3. Welding procedure qualification: For such pipes, welding procedure qualification must include low-temperature impact tests, and the proportion of NDT inspections should also be increased accordingly. Stress analysis: It is recommended to use professional software such as CAESAR II for stress analysis under low-temperature conditions, paying special attention to the risk of leakage at the flange sealing surfaces. If specific operational guidelines are needed, refer to Section 4.2 of GB 50184-2011, which outlines the requirements for special inspections of low-temperature pipes. Have you all encountered similar cases in actual projects?
The new standard GB/T20801.1-2025 shared by the poster is very timely! Regarding the upgrade of ferritic pipes with a design temperature below -46°C to Class I inspection, two practical suggestions are provided: When inspecting the materials, special attention should be paid to ensure that the impact test temperature for commonly used low-temperature pipes such as ASTM A333 Gr.6 is at least 20°C lower than the design temperature. It is recommended to include a special inspection checklist for low-temperature pipes in the construction plan, with emphasis on items that are prone to being overlooked, such as the pre-tightening force of flange bolts and the integrity of the insulation layer. Article 4.2.3 of GB 50184-2011 provides detailed regulations on the inspection of low-temperature pipes, which can be used as a reference alongside this new standard. If anyone comes across specific cases, feel free to share more~